ISBN 9783843947633

978-3-8439-4763-3, Reihe Physik

José Antonio Vargas Roco
Non-equilibrium dynamics of ultracold quantum gases in higher bands of an optical lattice

176 Seiten, Dissertation Universität Hamburg (2021), Softcover, B5

Zusammenfassung / Abstract

In this thesis novel experiments of non-equilibrium dynamics of ultracold quantum gases populating higher bands of a bipartite square optical lattice are performed.

The emergence of metastability is observed in the second band of the lattice. This phenomenon is experimentally investigated through the relaxation dynamics of atoms towards the lowest band.

Three different stages are identified. A metastable stage arises which is characterized by a slow decay of the total atom number from the first excited band. An explanation for the experimental measurements is given by a theoretical model which treats the Hamiltonian of the system in the tight-binding approximation for the first four energy bands. The simulations show that the condensate state, which presents a chiral phase, i.e. a complex superposition of p-orbitals px ± ipy, inhibits decay to the lowest band by destructive interference in the two main decay channels.

The observation of single-particle dynamics such as Bloch oscillations in the lowest and second band of the lattice is carried out. In addition, with the support of Bloch oscillations, a BEC is selectively prepared in one of the two degenerate energy minima, i.e. the X-points in the second band. A subsequent oscillation between the population of the X-points is experimentally measured corresponding to the first observation of Josephson-like dynamics in higher bands. The oscillation frequency scales with the ratio between two collision parameters: the conventional on-site contact interaction from the Hubbard model g0 and a collision term which exhibits orbital flavour changing g1. In the experiment, the value of g1/g0 is connected to the potential difference ∆V . The measurements are compared with simulations given by two models: a quantum model which solely two single-particle modes are accounted for and the multi-band tight-binding approach of the system.